Robert S Walker

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• PhD
• Professor at University of Missouri

European expansion and contact with indigenous populations led to catastrophic depopulation primarily through the introduction of novel infectious diseases to which native peoples had limited exposure and immunity. In the Amazon Basin such contacts continue to occur with more than 50 isolated indigenous societies likely to make further contacts wit...

There are about 50 isolated indigenous societies across lowland South America, with limited to no contact with the outside world. Despite displacements , epidemics, and hostile interactions with outsiders, such tribes still manage to survive. How can we ensure the well-being of humanity's last known isolated peoples under such enormous and mounting...

The headwaters of the Amazon Basin harbor most of the world's last indigenous peoples who have limited contact with encroaching colonists. Knowledge of the geographic distribution of these isolated groups is essential to assist with the development of immediate protec-tions for vulnerable indigenous settlements. We used remote sensing to document t...

Contemporary humans exhibit spectacular biological success derived from cumulative culture and cooperation. The origins of these traits may be related to our ancestral group structure. Because humans lived as foragers for 95% of our species' history, we analyzed co-residence patterns among 32 present-day foraging societies (total n = 5067 individua...

Humans often display extensive forms of prosocial behavior, frequently beyond what is predicted by inclusive fitness. This observation has led to various models attempting to explain the unique extent of human altruism. While many of these models have been empirically tested, one model, the ancestor–descendant conflict model, which is based on a ma...

Open-air accumulations of chipped stone debris are a common feature in arid landscapes, yet despite their prevalence, such archives are often dismissed as uninformative or unreliable. In the canyonlands of Dhofar, southern Oman, lithic surface scatters are nearly ubiquitous, including extensive, multi-component workshops associated with chert outcr...

Topographic relief potentially played an important role in Stone Age hunting from the Middle Paleolithic onwards. Natural physical features like arroyos and cliffs, among many others, likely served as traps to stop or hinder animal movement. Yet, the presence of elevation and slope variation on a landscape means that hunters also may have been able...

Human lifestyles vary enormously over time and space and so understanding the origins of this diversity has always been a central focus of anthropology. A major source of this cultural variation is the variation in institutional complexity: the cultural packages of rules, norms, ontologies and expectations passed down through societies across gener...

Mobility, food storage, and population density are central to the movement ecology of hunter-gatherer populations and understanding how these lifestyle traits covary over time and space has long been of interest to archaeologists and anthropologists. An important question that remains unresolved is the conditions under which hunter-gatherer populat...

Fundamental frequency ( f o ) is the most perceptually salient vocal acoustic parameter, yet little is known about how its perceptual influence varies across societies. We examined how f o affects key social perceptions and how socioecological variables modulate these effects in 2,647 adult listeners sampled from 44 locations across 22 nations. Low...

Amazonia is an invaluable global asset for all its ecological and cultural significance. Indigenous peoples and their lands are pivotal in safeguarding this unique biodiversity and mitigating global climate change. Understanding the causal structure behind variation in the degree of environmental conservation across different indigenous lands–each...

Bullet ricochets are common occurrences during shooting incidents and can provide a wealth of information useful for shooting incident reconstruction. However, there have only been a small number of studies that have systematically investigated bullet ricochet impact site morphology. Here, this study reports on an experiment that examined the plan-...

Isolated indigenous societies who actively avoid sustained peaceful contact with the outside world are critically endangered. Last year, “Tanaru”, the lone surviving man of his tribe for at least 35 years, died in Southwest Amazonia, marking the latest cultural extinction event in a long history of massacres, enslavement, and epidemics. Yet in the...

Isolated indigenous societies who actively avoid sustained peaceful contact with the outside world are critically endangered. Last year, "Tanaru", the lone surviving man of his tribe for at least 35 years, died in Southwest Amazonia, marking the latest cultural extinction event in a long history of massacres, enslavement, and epidemics. Yet in the...

Stone Age hunter-gatherers likely often had choices concerning the raw materials used in the production of their technologies. How different raw materials performed once transformed into tools was one potential consideration that influenced raw material choices. Here, we present an experiment comparing replica Late Pleistocene North American Clovis...

This study is an assessment of Clovis spear thrusting penetration depth and entry wound size. Thiswork is the fifth contribution in a series of experiments aimed at shedding light on the functionalperformance of distinct Clovis point forms. Here, using highly controlled and standardizedprocedures, we had a participant who had previously trained wit...

This study examines the fluting of two well‐known Late Pleistocene fluted point types in North America: Clovis and Folsom. Using scaling analyses, we assess the changing relationship between flute length and point length in a large sample of each type. Researchers use scaling to investigate the physical constraints of an object and determine how it...

The evolution of the hominin hand has been widely linked to the use and production of flaked stone tool technologies. After the earliest handheld flake tools emerged, shifts in hominin hand anatomy allowing for greater force during precision gripping and ease when manipulating objects in-hand are observed in the fossil record. Previous research has...

The atlatl is a handheld, rod-shaped device that employs leverage to launch a dart, and represents a major human technological innovation. One hypothesis for forager atlatl adoption over its presumed predecessor, the thrown javelin, is that a diverse array of people could achieve equal performance results, thereby facilitating inclusive participati...

Isolated indigenous societies who actively avoid sustained peaceful contact with the outside world are critically endangered. Last year “Tanaru”, the lone surviving man of his tribe for at least 35 years, died in Southwest Amazonia marking the latest cultural extinction event in a long history of massacres, enslavement, and epidemics. Yet in the up...

Amazonia has as least two major centers of ancient human social complexity, but the full geographic extents of these centers remain uncertain. Across the southern rim of Amazonia, over 1,000 earthwork sites comprised of fortified settlements, mound villages, and ditched enclosures with geometric designs known as geoglyphs have been discovered. Qual...

Researchers use a variety of target materials, and sometimes combinations of materials, in their archaeological experiments to examine thrust‐spear or projectile penetration, impact angle, durability, and other issues involving prehistoric hunting weaponry. This variety of target materials is beneficial to archaeological science in several ways, bu...

Stone‐tipped weaponry was important to the survival of past peoples, and many functional and non‐functional factors likely influenced their design. Two functional factors that past peoples likely considered in the design of their stone tips are durability (whether a stone tip breaks or not) and robusticity (how much damage is incurred upon breakage...

Stone lanceolate projectile points are characterized as having a lance shape with a tip tapering to an apex and are found in the archaeological record at different times and places across the world. In North America, lanceolate points are an important component of the Paleoindian period. One of the main factors in the design of lanceolate points is...

Experimental archaeology continues to mature methodologically and theoretically. Around the world, practitioners are increasingly using modern materials that would have been unavailable to prehistoric people in archaeological experiments. The use of a modern material substitute can offer several benefits to experimental method, design, control, rep...

Stone that fractured conchoidally was an important resource for prehistoric hunter‐gatherers. In recent years, archaeologists have come to realize that rather than defining stone “quality” simply and implicitly as “high” or “low,” a stone's quality can be best defined in several different explicit and often quantitative ways involving production, f...

This study is an experimental assessment of Clovis knife use. This work is the third contribution in a series of experiments aimed at shedding light on the functional performance of distinct Clovis “point” forms. Here, we used seven replica Clovis point forms, representing the average and extremes of observed Clovis form, in two cutting tasks: rope...

Estimating the total human population size (i.e., abundance) of the preagricultural planet is important for setting the baseline expectations for human-environment interactions if all energy and material requirements to support growth, maintenance, and well-being were foraged from local environments. However, demographic parameters and biogeographi...

Abstract Across the planet the biogeographic distribution of human cultural diversity tends to correlate positively with biodiversity. In this paper we focus on the biogeographic distribution of mammal species and human cultural diversity. We show that not only are these forms of diversity similarly distributed in space, but they both scale superli...

In Late Pleistocene North America colonizing hunter-gatherers knapped and used Clovis fluted projectile points. During their expansion the size and shape of Clovis points changed significantly. Archaeologists know that cultural drift contributed to this variation, but is it possible that this single source could alone generate so much variation so...

Comparative phylogenetic analyses based on linguistic data are useful for reconstructing the cultural evolution of recent expansions of humans around the world. It is an exciting time for phylogenetic comparative studies in lowland South America given the emergence of more comprehensive ethnolinguistic datasets. Phylogenetic methods can now be appl...

How did languages spread across the globe? Why do we sometimes find large language families, distributed over a wider area, and sometimes clusters of very small families or language isolates (i.e. languages without known relatives)? What was the role of agriculture in language spread? What do different language ideologies and patterns of ethnic ide...

Human societies exhibit a diversity of social organizations that vary widely in size, structure, and complexity. Today, human sociopolitical complexity ranges from stateless small-scale societies of a few hundred individuals to complex states of millions, most of this diversity evolving only over the last few hundred years. Understanding how sociop...

The human species is diverse in the size, structure and complexity of our social organizations. Today, human sociopolitical complexity ranges from stateless small-scale societies to complex states that integrate millions of individuals over vast geographic areas. Here, we explore major transitions across this range of complexity. In particular, we...

Group living is common in mammals, particularly in primates and humans. Across species, groups are social networks where co-residing members exchange information and balance trade-offs between competition and cooperation for space, resources, and reproductive opportunities. From a macroecological perspective, species-specific group sizes are ultima...

The expansion of the human species out of Africa in the Pleistocene, and the subsequent development of agriculture in the Holocene, resulted in waves of linguistic diversification and replacement across the planet. Analogous to the growth of populations or the speciation of biological organisms, languages diversify over time to form phylogenies of...

The expansion of the human species out of Africa in the Pleistocene, and the subsequent development of agriculture in the Holocene, resulted in waves of linguistic diversification and replacement across the planet. Analogous to the growth of populations or the speciation of biological organisms, languages diversify over time to form phylogenies of...

The expansion of the human species out of Africa in the Pleistocene, and the subsequent development of agriculture in the Holocene resulted in waves of linguistic diversification and replacement across the planet. Analogous to the growth of populations or the speciation of biological organisms, languages diversify over time to form phylogenies of l...

Background The world’s last uncontacted indigenous societies in Amazonia have only intermittent and often hostile interactions with the outside world. Knowledge of their locations is essential for urgent protection efforts, but their extreme isolation, small populations, and semi-nomadic lifestyles make this a challenging task. Methods Remote sens...

Background. The world’s last uncontacted indigenous societies in Amazonia have only intermittent and often hostile interactions with the outside world. Knowledge of their locations is essential for urgent protection efforts, but their extreme isolation, small populations, and semi-nomadic lifestyles make this a challenging task. Methods. Remote sen...

Background. The world’s last uncontacted indigenous societies in Amazonia have only intermittent and often hostile interactions with the outside world. Knowledge of their locations is essential for urgent protection efforts, but their extreme isolation, small populations, and semi-nomadic lifestyles make this a challenging task. Methods. Remote sen...

Short-term hunter-gatherer residential camps have been a central feature of human settlement patterns and social structure for most of human evolutionary history. Recent analyses of ethnohistoric hunter-gatherer data show that across different environments, the average size of hunter-gatherer bands is remarkably constant and that bands are commonly...

Background: All biological populations exhibit fluctuations in size over time due to stochastic variation in growth rates that result in local extinctions, but these dynamics are poorly understood in traditional human populations. Here, we explore extinction processes over human evolutionary history due to the effects of (i) demographic stochastici...

Partible paternity, the belief that a child can have more than one biological father, is widespread in lowland South America. An analysis of demographic data sets from four lowland tribes (Aché, Barí, Ese Eja, and Surui) reveals a systematic variation in the sex ratios of live births with respect to the number of fathers to whom the births are attr...

In many primates, including humans, the vocalizations of males and females differ dramatically, with male vocalizations and vocal anatomy often seeming to exaggerate apparent body size. These traits may be favoured by sexual selection because low-frequency male vocalizations intimidate rivals and/or attract females, but this hypothesis has not been...

At least 50 indigenous groups spread across lowland South America remain isolated and have only intermittent and mostly hostile interactions with the outside world. Except in emergency situations, the current policy of governments in Brazil, Colombia, and Peru towards isolated tribes is a “leave them alone” strategy, in which isolated groups are le...

High-resolution imagery information. Here is the information for the recent high-resolution satellite imagery purchased from DigitalGlobe and used for heads-up digitization for each site (PAN = panchromatic, MS = multispectral). We compared the total cleared area with Global Forest Change areas using cumulative estimates over the previous 3 years w...

Studies of cultural adaptation and evolution are important for advancing our knowledge of what it means to be human and helping to move us toward a richer explanation of human variation. Considerable progress has been made in understanding cultural evolution using linguistic phylogenies to track the evolution of inheritance, residence, kinship, mar...

Objectives: Genealogies contain information on the prevalence of different sibling types that result from past reproductive behavior. Full sibling sets stem from stable monogamy, paternal half siblings primarily indicate male reproductive skew, and maternal half siblings reflect unstable pair bonds. Methods: Full and half sibling types are calcu...

This essay addresses the significance and evidence surrounding the debate about how hunter-gatherers and other humans organize their residential groups. In most species of mammals, either males or female remain in their natal group (the philopatric sex) while the other sex disperses at maturity (the dispersing sex). Sex-biased philopatry and disper...

Partible paternity refers to the conception belief that children can have multiple fathers (" co-fathers ") and is common to indigenous cultures of lowland South America. The nature of social relationships observed between co-fathers reveals information about the reproductive strategies underlying partible paternity. Here we analyze clan, genealogi...

Partible paternity refers to the conception belief that children can have multiple fathers (“co-fathers”) and is common to indigenous cultures of lowland South America. The nature of social relationships observed between co-fathers reveals information about the reproductive strategies underlying partible paternity. Here we analyze clan, genealogica...

Partible paternity refers to the conception belief that children can have multiple fathers (“co-fathers”) and is common to indigenous cultures of lowland South America. The nature of social relationships observed between co-fathers reveals information about the reproductive strategies underlying partible paternity. Here we analyze clan, genealogica...

Partible paternity refers to the conception belief that children can have multiple fathers (“co-fathers”) and is common to indigenous cultures of lowland South America. The nature of social relationships observed between co-fathers reveals information about the reproductive strategies underlying partible paternity. Here we analyze clan, genealogica...

The vast forests on the border between Brazil and Peru harbour a number of indigenous groups that have limited contact with the outside world. Accurate estimates of population sizes and village areas are essential to begin assessing the immediate conservation needs of such isolated groups. In contrast to overflights and encounters on the ground, re...

Significance Humans, like chimpanzees, engage in coalitionary violence: Members of both species coordinate lethal activity against conspecifics. The origin and adaptive functions of this behavior are poorly understood, and data from tribal populations are rare. We examine the composition of lethal coalitions from the Yanomamö, a tribal society in A...

Hypotheses on the benefits of the practice of partible paternity are tested using demographic data for Ache foragers of Paraguay. Partible paternity refers to the institution of multiple males considered to contribute to the conception of a single offspring. Analyses focus on patterns of primary and secondary co-fatherhood among men, genealogical r...

The relatedness of human groups has important ramifications for kin (group) selection to favor more collective action and invites the potential for more exploitation by political leaders. Endogamous marriages among kin create intensive kinship systems with high group relatedness, while exogamous marriages among nonrelatives create extensive kinship...

Fissions of human communities are monumental occasions with consequences for cultural and genetic variation and divergence through time by means of serial founder effects. An ethnographic review shows that most human group fissions are fueled primarily by internal political conflict and secondarily by resource scarcity. As found for other social an...

Objectives: Greater Amazonia harbors as many as 100 locations of isolated indigenous peoples. Few options are available to assess the demographic health of these populations given their limited contact with the outside world. Remote sensing offers one option. Methods: An isolated village in Brazil near the Peruvian border is visible with Google...

Social norms that regulate reproductive and marital decisions generate impressive cross-cultural variation in the prevalence of kin marriages. In some societies, marriages among kin are the norm and this inbreeding creates intensive kinship networks concentrated within communities. In others, especially forager societies, most marriages are between...

Marriages among kin have the dual effect of both increasing average group relatedness as well as reducing the total number of kin by eliminating more genealogically and geographically distant individuals from kinship networks. Marriage decisions therefore face a tradeoff between density of kin, or formation of intensive kinship systems, and the div...

Lowland South America has long been a battle-ground between European colonization and indigenous survival. Initial waves of European colonization brought disease epidemics, slavery, and violence that had catastrophic impacts on indigenous cultures. In this paper we focus on the demography of 238 surviving populations in Brazil. We use longitudinal...

The current study assessed the heritability of personality in a traditional natural-fertility population, the Ache of eastern Paraguay. Self-reports (n = 110) and other-reports (n = 66) on the commonly used Big Five Personality Inventory (i.e., extraversion, agreeableness, conscientiousness, neuroticism, openness) were collected. Self-reports did n...

Assortative Mating. Both of these relations remain significant after controlling for age. Also, after simultaneously removing the two couples in the sample for which both members were interviewed by the research assistant, both relations remained significant. (TIFF)

Lowess Function of Reproductive Success by Age. This Lowess curve (tension = 2/3) is a more flexible way to account for nonlinear variation than including quadratic components in regression analyses; however, the interpretation of results below did not differ if quadratic components rather than the Lowess values were used as controls. (TIFF)

Postmarital residence patterns in traditional human societies figure prominently in models of hominid social evolution with arguments for patrilocal human bands similar in structure to female-dispersal systems in other African apes. However, considerable flexibility in hunter-gatherer cultures has led to their characterization as primarily multiloc...

Violence was likely often a strong selective pressure in many traditional lowland South American societies. A compilation of 11 anthropological studies reporting cause of death shows that violence led to about 30% of adult deaths, of which about 70% were males. Here violent deaths are further itemized at the level of ethnographically-reported death...

Question: The language-farming dispersal hypothesis postulates that the current bio-geographic distribution of global ethnolinguistic diversity is due to prehistoric demic expansions of agricultural populations. Does human population size increase as diet is increasingly based on agriculture, and is this relation moderated by agricultural potential...

This paper discusses phylogenetic reticulation using linguistic data from the Automated Similar-ity Judgment Program or ASJP (Holman et al., 2008; Wichmann et al., 2010a). It contributes methodologically to the examination of two measures of reticulation in distance-based phylo-genetic data, specifically the δ score of Holland et al. (2002) and the...

Recent advances in automated assessment of basic vocabulary lists allow the construction of linguistic phylogenies useful for tracing dynamics of human population expansions, reconstructing ancestral cultures, and modeling transition rates of cultural traits over time. Here we investigate the Tupi expansion, a widely-dispersed language family in lo...

Comparisons between expert classifications and ASJP trees for the Tupi-Guarani subgroup. (DOCX)

On the internal classification of Tupi-Guarani. (DOCX)

Tupi cultural traits with possible states (top table) and data codings (bottom table). (DOCX)

IntroductionComparative Human Population EcologyComparative Human Life HistoryHuman Ecological and Evolutionary EnergeticsConclusions

Previous studies have examined tooth eruption as it relates intrinsically to body mass, brain mass, and other life history variables, and extrinsically to ecological factors (e.g., age at foraging independence, environmental risk aversion, and maternal investment). Different models have been explored wherein each of these variables impacts ontogeny...

Humans evolved to withstand harsh environments by adaptively decreasing their body size. Thus, adaptation to a hostile environment defers the infancy-childhood transition age (ICT), culminating in short stature. In natural-fertility human societies, this transition is associated with weaning from breastfeeding and the mother's new pregnancy. We the...

The age of puberty has fallen over the past 130 years in industrialized, western countries, and this fall is widely referred to as the secular trend for earlier puberty. The current study was undertaken to test two evolutionary theories: (a) the reproductive system maximizes the number of offspring in response to positive environmental cues in term...

This paper discusses phylogenetic reticulation using linguistic data from the Automated Similar-ity Judgment Program or ASJP (Holman et al., 2008; Wichmann et al., 2010a). It contributes methodologically to the examination of two measures of reticulation in distance-based phylo-genetic data, specifically the δ score of Holland et al. (2002) and the...

The universality of marriage in human societies around the world suggests a deep evolutionary history of institutionalized pair-bonding that stems back at least to early modern humans. However, marriage practices vary considerably from culture to culture, ranging from strict prescriptions and arranged marriages in some societies to mostly unregulat...

Phylogenetic inference based on language is a vital tool for tracing the dynamics of human population expansions. The timescale of agriculture-based expansions around the world provides an informative amount of linguistic change ideal for reconstructing phylogeographies. Here we investigate the expansion of Arawak, one of the most widely dispersed...

Reconstructing the rise and fall of social complexity in human societies through time is fundamental for understanding some of the most important transformations in human history. Phylogenetic methods based on language diversity provide a means to reconstruct pre-historic events and model the transition rates of cultural change through time. We mod...

Partible paternity, the conception belief that more than one man can contribute to the formation of a fetus, is common in lowland South America and characterized by nonexclusive mating relationships and various institutionalized forms of recognition and investment by multiple cofathers. Previous work has emphasized the fitness benefits for women wh...

Lifetime reproductive effort (LRE) measures the total amount of metabolized energy diverted to reproduction during the lifespan. LRE captures key components of the life history and is particularly useful for describing and comparing the life histories of different organisms. Given a simple energetic production constraint, LRE is predicted to be sim...

The biogeographic expansion of modern humans out of Africa began approximately 50,000 years ago. This expansion resulted in the colonization of most of the land area and habitats throughout the globe and in the replacement of preexisting hominid species. However, such rapid population growth and geographic spread is somewhat unexpected for a large...

Previous attempts to explain variation in human growth and development emphasize the energetic constraints imposed by malnutrition and disease. However, this approach does not address the evolutionary effects of mortality risk on ontogenetic variation, a common theme in life‐history studies. The conventional approach can be reconciled with life‐his...